Lazy, selfish and ignorant. But that is just my first thought right after I finished reading it.
It really depends on that person cooking. Knowing very well that 1 of them is a vegetarian, then why invite or rather why not cook a separate dish? Why did she choose the dish that needs the fish sauce? It is definitely not ethical at all. And the funny part was, knowing that her friend will not consume it then why bother having the dilemma?
Haha... Well, these are just my thoughts. At one time, I had a dilemma too, whether to consume the meat my friend cooked tirelessly the whole day.